Add structure provider for string literals

src/EditorFeatures/CSharpTest/Structure/StringLiteralExpressionStructureTests.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CSharp.Structure;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Structure;
+using Microsoft.CodeAnalysis.Test.Utilities;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Structure
+{
+    public class StringLiteralExpressionStructureTests : AbstractCSharpSyntaxNodeStructureTests<LiteralExpressionSyntax>
+    {
+        internal override AbstractSyntaxStructureProvider CreateProvider() => new StringLiteralExpressoinStructureProvider();
+
+        [Fact, Trait(Traits.Feature, Traits.Features.Outlining)]
+        public async Task TestVerbatimString()
+        {
+            await VerifyBlockSpansAsync(
+@"
+class C
+{
+    void M()
+    {
+        var v =
+{|hint:{|textspan:$$@""
+class 
+{
+}
+""|}|};
+    }
+}",
+                Region("textspan", "hint", CSharpStructureHelpers.Ellipsis, autoCollapse: true));
+        }
+    }
+}

src/Features/CSharp/Portable/Structure/Providers/StringLiteralExpressoinStructureProvider.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Threading;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Options;
+using Microsoft.CodeAnalysis.PooledObjects;
+using Microsoft.CodeAnalysis.Structure;
+
+namespace Microsoft.CodeAnalysis.CSharp.Structure
+{
+    internal sealed class StringLiteralExpressoinStructureProvider : AbstractSyntaxNodeStructureProvider<LiteralExpressionSyntax>
+    {
+        protected override void CollectBlockSpans(LiteralExpressionSyntax node, ArrayBuilder<BlockSpan> spans, OptionSet options, CancellationToken cancellationToken)
+        {
+            if (node.IsKind(SyntaxKind.StringLiteralExpression))
+            {
+                spans.Add(new BlockSpan(
+                    isCollapsible: true,
+                    textSpan: node.Span,
+                    hintSpan: node.Span,
+                    type: BlockTypes.Expression,
+                    autoCollapse: true,
+                    isDefaultCollapsed: false));
+            }
+        }
+    }
+}